Method for producing carboxylic acid

ABSTRACT

An aldehyde-containing oily solution and an aqueous hydrogen peroxide solution are reacted in the presence of a catalyst comprising a polymer compound having a sulfonic acid group in a side chain thereof in a heterogeneous solution system. According to such a reaction process, carboxylic acid can be efficiently produced under mild conditions having very little influence and toxicity on the environment and a human body, with simple operations, without requiring the operation for removing a solvent after the completion of the reaction.

TECHNICAL FIELD

The present invention relates to a process for producing carboxylic acidwhich is an important intermediate in the synthesis of diesters,polyesters and polyamides which are useful substances to be widelyutilized in various industrial fields including chemical industries asplasticizers, lubricants, heat transfer media, dielectric media, fibers,copolymers, coating resins, surfactants, fungicides, insecticides,adhesives, and the like. More specifically, the present inventionrelates to a process for producing carboxylic acid by the reaction ofaldehyde-containing oily solution with an aqueous hydrogen peroxidesolution.

BACKGROUND ART

As processes for producing carboxylic acid by oxidizing aldehyde,reactions using potassium permanganate, manganese dioxide or silveroxide as an oxidizing agent are known. However, these processes load alarge burden on the environment in view of the generation of highlytoxic by-products, the corrosiveness of the oxidizing agents, and thelike, so that it is hard to say that they are industrially excellentprocesses.

On the other hand, oxygen and hydrogen peroxide are inexpensive andnon-corrosive, and no by-product is formed or a by-product is harmlesswater after the reactions, so that an environmental burden is small andthus it can be said that they are excellent oxidizing agents forindustrial utilization.

Although processes for forming carboxylic acid from aldehyde usingoxygen as an oxidizing agent is known (Non-Patent Document 1), in theseprocesses, an acid, a base, or benzene is used as a solvent in thepresence of a heavy metal catalyst such as silver or copper. Moreover,it is also reported that an oxidation reaction of aldehyde with oxygencatalyzed by nickel complex proceeds under mild conditions (Non-PatentDocument 2), but it is necessary to use cyclohexanone, acetone, or thelike as a solvent.

On the other hand, as processes for producing carboxylic acid fromaldehyde using hydrogen peroxide as an oxidizing agent, there are knowna process of using an equivalent amount of hexafluoroacetone in amethylene chloride solvent (Non-Patent Document 3) and a process ofusing formic acid as a solvent (Non-Patent Document 4).

Moreover, as processes for producing carboxylic acid utilizing catalyticoxidation reactions using hydrogen peroxide as an oxidizing agent, thereare reported a process of forming a methyl ester using 28% of a sulfuricacid catalyst in a methanol solvent (Non-Patent Document 5), a processof using 5% of a PhSeOOH catalyst in a THF solvent (Non-Patent Document6), a process of using a catalytic amount (0.9%) of HBr using dioxane asa solvent (Non-Patent Document 7), and a process of using 5% of an SeO₂catalyst in a THF solvent (Non-Patent Document 8). In all thesereactions, a water-soluble solvent which forms a homogeneous phase withan aqueous hydrogen peroxide solution, such as formic acid, methanol,THF or dioxane, is used as a solvent.

Thus, in the oxidation reactions of a water-insoluble aldehyde, the useof polar organic solvents as mentioned above is indispensable in orderto form a homogeneous solution by dissolving a water-insoluble aldehydein an aqueous hydrogen peroxide solution. As a result, at the isolationof carboxylic acid which is an objective product, a means for removingthe polar organic solvents is necessary and reaction operations andapparatus become complex. Furthermore, the influence and toxicity of theorganic solvents themselves on the environment and a human body havebeen pointed out.

Non-Patent Document 1: Ind. Eng. Chem., 42 768-776 (1950)

Non-Patent Document 2: Chem. Lett., 5-8 (1991)

Non-Patent Document 3: Tetrahedron Lett., 21, 685-688 (1980)

Non-Patent Document 4: Synthesis, 21, 295-297 (1993)

Non-Patent Document 5: J. Org. Chem., 49, 4740-4741 (1984)

Non-Patent Document 6: Tetrahedron Lett., 29, 1967-1970 (1988)

Non-Patent Document 7: Specification of European Patent No. 424,242

Non-Patent Document 8: Synth. Commun., 30, 4425-4434 (2000)

DISCLOSURE OF THE INVENTION

The present invention has been performed for overcoming the aboveproblems of the conventional technologies, and an object thereof is toprovide a safe, simple and efficient process for producing carboxylicacid by the reaction of aldehyde with an aqueous hydrogen peroxidesolution, which enables the production of the carboxylic acid in highyields under mild reaction conditions as well as which dose not requirethe operation for removing a solvent after the completion of thereaction with simple reaction operations and is very little in influenceand toxicity on the environment and a human body.

As a result of the extensive studies for solving the above problems, thepresent inventors have found that, instead of the conventional reactionprocess of carrying out an oxidation reaction in a homogeneous solutionsystem of a nonaqueous aldehyde solution and an aqueous hydrogenperoxide solution in a polar organic solvent, the selection of thereaction using an heterogeneous solution system of an aqueous hydrogenperoxide solution and a water-insoluble aldehyde-containing oilysolution in the presence of a polymer sulfonic acid catalyst enables thesafe and simple production of the corresponding carboxylic acid in highyields, unlike the conventional common technical findings. Thus, theyhave accomplished the present invention.

Namely, the present invention provides the followings:

(1) A process for producing carboxylic acid, which comprises reactingaldehyde-containing oily solution with an aqueous hydrogen peroxidesolution in the presence of a catalyst comprising a polymer compoundhaving a sulfonic acid group in a side chain thereof in a heterogeneoussolution system.

(2) The process for producing carboxylic acid according to the above(1), wherein the polymer compound is at least one polymer selected froma styrene polymer, a copolymer of styrene and divinylbenzene, and afluorocarbon polymer.

(3) The process for producing carboxylic acid according to the above (1)or (2), wherein the aldehyde is a compound represented by the followingformula (1):RCHO  (1)wherein R represents a monovalent group selected from hydrogen, an alkylgroup, a cycloalkyl group, an aryl group, and an aralkyl group.

BEST MODE FOR CARRYING OUT THE INVENTION

The process for producing carboxylic acid by the oxidation reaction ofaldehyde using hydrogen peroxide according to the present invention ischaracterized in that the oxidation reaction is carried out in aheterogonous solution of an aqueous hydrogen peroxide solution andaldehyde-containing oily solution in the presence of a catalystcomprising a polymer compound having a sulfonic acid group in a sidechain thereof.

Hitherto, in a liquid-liquid reaction, when starting materialsthemselves or a starting material and reaction reagents such as anoxidizing agent and a reaction accelerator have no compatibility witheach other, it is advantageous in view of the selectivity, yield and thelike to use a process of preparing a homogeneous solution of bothsubstances beforehand using a solvent in which the starting material(s)and the reaction reagent(s) mutually dissolve for smooth progress of thereaction and subsequently reacting them.

Even in the reaction of synthesizing carboxylic acid by the reaction ofaldehyde with hydrogen peroxide, as mentioned above, following thisconcept, there has been adopted a process for producing carboxylic acidby reacting a homogeneous solution of a water-insoluble aldehyde andhydrogen peroxide using a polar solvent in the presence of an acidcatalyst.

As a result of seeking various studies, experiments and theoreticalconsideration on such an oxidation reaction from the viewpoint of moreefficient protection of the environment and a human body, the presentinventors have found that the yield of the carboxylic acid is remarkablyimproved and also a remarkable contribution to the reduction of anenvironmental burden is achieved when the oxidation reaction of aldehydeusing hydrogen peroxide as an oxidizing agent is carried out not in ahomogeneous solution system, but in a heterogeneous solution system ofthe aldehyde-containing oily solution and the aqueous hydrogen peroxidesolution unlike the conventional technical common knowledge and in thepresence of a catalyst comprising a polymer compound having a sulfonicacid group in a side chain thereof. Such a finding cannot be expectedbased on the conventional common technical knowledge, but is a specificphenomenon which is first found as a result of accumulated sedulousexperiments and studies by the inventors.

As the starting material for use in the process of the presentinvention, a hitherto known common aldehyde can be used and the materialis not particularly limited, but the aldehyde represented by thefollowing formula (1) is preferably used.RCHO  (1)wherein R has the same meaning as described above.

When R is an alkyl group, the number of the carbon atoms of the alkylgroup is from 3 to 22, preferably from 5 to 18. Examples of the alkylgroup include an octyl group, a 2-ethylhexyl group, and the like. When Ris a cycloalkyl group, the number of the carbon atoms of the cycloalkylgroup is from 5 to 12, preferably from 5 to 8. Examples of thecycloalkyl group include a cyclohexyl group, a cyclooctyl group, and thelike. When R is an aryl group, the number of the carbon atoms of thearyl group is from 6 to 14, preferably from 6 to 10. Examples of thearyl group include a phenyl group, a naphthyl group, and the like. WhenR is an aralkyl group, the number of the carbon atoms of the aralkylgroup is from 7 to 15, preferably from 7 to 11. Examples of the aralkylgroup include a benzyl group, a phenethyl group, a naphthylmethyl group,and the like. Even when R is any of an alkyl group, a cycloalkyl group,an aryl group and an aralkyl group, the alkyl group, cycloalkyl group,aryl group and aralkyl group may be further substituted with asubstituent(s) such as a hydrocarbon group, an alkoxy group, an aryloxygroup, a cyano alkyl, a trimethylsilyl group or a hydroxy group.Moreover, when a formyl group and an olefin coexist in a molecule,olefincarboxylic acid obtained by selective oxidation of the formylgroup is obtained.

Examples of the aldehyde to be preferably used in the present inventioninclude octyl aldehyde, 3-phenylpropionaldehyde, 2-ethylhexyl aldehyde,trimethylacetaldehyde, 2-phenylpropionaldehyde, bezaldehyde,p-tolualdehyde, p-anisaldehyde, 10-undecenaldehyde, and the like.

In the present invention, as mentioned above, since it is an object toprovide a safe, simple and efficient process for producing carboxylicacid from aldehyde by the reaction of the aldehyde with an aqueoushydrogen peroxide solution, which enables the production of thecarboxylic acid from the aldehyde in high yields under mild reactionconditions as well as which dose not require the operation for removinga solvent after the completion of the reaction with simple reactionoperations and is very little in influence and toxicity on theenvironment and a human body, an oily solution of the aldehyde itselfand also an oily solution of the aldehyde dissolved in a non-polarsolvent such as hydrocarbon which is not compatible with water may bementioned as the aldehyde-containing oily solution. However, in view ofthe above reduction of environmental burden and the operation forremoving the solvent, it is most preferable to use a water-insolublealdehyde itself.

The oxidizing agent for use in the process of the present invention ishydrogen peroxide, which is used in an aqueous solution thereof at theapplication. The concentration of the aqueous hydrogen peroxide solutionis not particularly limited since the oxidation reaction of the aldehydeoccurs according to the concentration, but the concentration isgenerally selected from the range of 1 to 80% by weight, preferably 30to 60% by weight.

Moreover, the amount of the aqueous hydrogen peroxide to be used is alsonot particularly limited, but is generally selected from the range of1.0 to 10.0 equivalents, preferably 1.0 to 1.2 equivalents, to thealdehyde.

The catalyst for use in the process of the present invention is acatalyst mainly comprising a polymer compound having a sulfonic acidgroup in a side chain thereof. The reaction of the present invention isremarkably accelerated by using, as such a catalyst, a polymer compoundwherein a sulfonic acid group is bound to a side chain thereof.

The polymer compound wherein a sulfonic acid group is bound to a sidechain thereof exhibits the effect as a catalyst even when the polymerpart has any structure, but a polymer compound which is insoluble inwater and an organic substance, for example, a styrene polymer, acopolymer of styrene and divinylbenzene, or a fluorocarbon polymerwherein a sulfonic acid group is bound to a side chain thereof ispreferably used. Examples of the polymer compound wherein a sulfonicacid group is bound to a side chain thereof include commerciallyavailable polymer compounds, such as Daiaion PK228 (manufactured byMitsubishi Chemical Corporation) as a styrene polymer, Amberlyst 15(manufactured by Organo Corporation) and MSC-1 (manufactured byMuromachi Technos Co., Ltd.) as styrene-divinylbenzene copolymers, andNafion NR50 (manufactured by Du Pont) and Nafion SAC13 (manufactured byDu Pont) as fluorocarbon resins.

With regard to the amount of the polymer compound wherein a sulfonicacid group is bound to a side chain thereof to be used as a catalyst,since the reaction is accelerated as the amount increases, the sulfonicacid group can be used in large excess as the equivalent ratio of thesulfonic acid group to the formyl group of the aldehyde. However,although it depends on the reaction temperature, even when theequivalent ratio of the sulfonic acid group to the formyl group is0.0001 to 0.2 equivalent, preferably 0.01 to 0.1 equivalent, it ispossible to achieve a high yield within a relatively short time.

The catalyst for use in the production process of the present inventionis mainly comprising the above polymer compound wherein a sulfonic acidgroup is bound to a side chain thereof, but, if necessary, it is alsopossible to use an auxiliary catalyst such as acetic acid, phosphoricacid, phosphate, sulfate, hydrogen sulfate or ammonium salt.

The reaction conditions of the process of the present invention are notparticularly limited, but the reaction is usually carried out at therange of 30 to 120° C., preferably 50 to 100° C. The reaction pressuremay be any of normal pressure, elevated pressure, and reduced pressure,but it is preferably carried out under normal pressure.

Moreover, in the production process of the present invention, the orderof the addition of the starting material, the oxidizing agent, and thecatalyst and the reaction mode are not particularly limited as far asthey comprise a process wherein the aqueous hydrogen peroxide solutionand the aldehyde form a heterogeneous solution in the reaction system.Usually, there is adopted a process wherein the aldehyde is added to theaqueous hydrogen peroxide solution mixed with the catalyst to form aheterogeneous mixture of the three substances beforehand and then theyare reacted with stirring.

In the production process of the present invention, by adopting theabove specific oxidation reaction process, from the aldehyde representedby formula (1), carboxylic acid such as a corresponding acid:RCO₂H  (2)wherein R has the same meaning as described above, can be obtained in ahigh yield.

Examples of the carboxylic acid to be obtained by the process of thepresent invention include octanoic acid, 3-phenylpropionic acid,2-ethylhexanoic acid, trimethylacetic acid, 2-phenylpropionic acid,bezoic acid, p-toluic acid, p-anisic acid, 10-undecenoic acid, and thelike. Among these, octanoic acid, 3-phenylpropionic acid,2-ethylhexanoic acid and the like are preferably synthesized.

In the process of the present invention, after the completion of theabove reaction, an objective carboxylic acid can be obtained in highyields with a high selectivity by concentrating the resulting mixedsolution containing the carboxylic acid and then separating andpurifying it by a usual process, such as recrystallization, distillationor sublimation. Moreover, the separation of the catalyst is easilyachieved by filtration of the reaction liquid or an operation similarthereto such as decantation and the recovered catalyst can be repeatedlyused by washing with water without further purification.

EXAMPLES

The present invention will be explained more specifically with referenceto the following Examples, but the present invention is by no meanslimited by these Examples.

Example 1

Nafion NR50 (500 mg), 30% aqueous hydrogen peroxide solution (1.3 mL, 11mmol), and octyl aldehyde (1.6 mL, 10 mmol) were mixed and stirred at90° C. for 2 hours. After the reaction solution was cooled to roomtemperature, the yield of octanoic acid by measurement of GLC was 93%.

Example 2

Nafion NR50 (500 mg), 30% aqueous hydrogen peroxide solution (1.3 mL, 11mmol), and octyl aldehyde (1.6 mL, 10 mmol) were mixed and stirred at90° C. for 2 hours. After the reaction solution was cooled to roomtemperature, the yield of octanoic acid by measurement of GLC was 93%.The Nafion NR50 was separated from the reaction solution by filtrationand washed with 5 mL of water for five times. Then, octyl aldehyde (1.6mL, 10 mmol) and a 30% aqueous hydrogen peroxide solution (1.3 mL, 11mmol) were added, followed by stirring at 90° C. for 2 hours. After thereaction solution was cooled to room temperature, the yield of octanoicacid by measurement of GLC was 92%.

Comparative Example 1

Dioxane (10 mL) was used as a solvent so that octyl aldehyde (1.6 mL, 10mmol) and 30% aqueous hydrogen peroxide solution (1.3 mL, 11 mmol)formed a homogeneous phase, followed by stirring at 90° C. for 2 hourswithout using any catalyst. After the reaction solution was cooled toroom temperature, the yield of octanoic acid by measurement of GLC was30%.

Comparative Example 2

As a result of carrying out the reaction in the same conditions withExample 1 except that dioxane (10 mL) was added beforehand so that octylaldehyde and the aqueous hydrogen peroxide solution formed a homogeneousphase, the yield of octanoic acid was 49%.

Example 3

Nafion NR50 (500 mg), 30% aqueous hydrogen peroxide solution (1.3 mL, 11mmol), and 3-phenylpropionaldehyde (1.3 mL, 10 mmol) were mixed andstirred at 90° C. for 2 hours. After the reaction solution was cooled toroom temperature, the yield of 3-phenylpropionic acid by measurement ofGLC was 92%.

Example 4

Nafion NR50 (500 mg), 30% aqueous hydrogen peroxide solution (1.3 mL, 11mmol), and 2-ethylhexyl aldehyde (1.6 mL, 10 mmol) were mixed andstirred at 90° C. for 2 hours. After the reaction solution was cooled toroom temperature, the yield of 2-ethylhexanoic acid by measurement ofGLC was 65%.

Example 5

Nafion NR50 (500 mg), 30% aqueous hydrogen peroxide solution (1.3 mL, 11mmol), and trimethylacetaldehyde (1.1 mL, 10 mmol) were mixed andstirred at 90° C. for 2 hours. After the reaction solution was cooled toroom temperature, the yield of trimethylacetic acid by measurement ofGLC was 32%.

Example 6

Nafion NR50 (500 mg), 30% aqueous hydrogen peroxide solution (1.3 mL, 11mmol), and 2-phenylpropionaldehyde (1.3 mL, 10 mmol) were mixed andstirred at 90° C. for 2 hours. After the reaction solution was cooled toroom temperature, the yield of 2-phenylpropionic acid by measurement ofGLC was 10%.

Example 7

Nafion NR50 (500 mg), 30% aqueous hydrogen peroxide solution (1.3 mL, 11mmol), and benzaldehyde (1.0 mL, 10 mmol) were mixed and stirred at 90°C. for 2 hours. After the reaction solution was cooled to roomtemperature, the yield of benzoic acid by measurement of GLC was 82%.

Example 8

Nafion NR50 (500 mg), 30% aqueous hydrogen peroxide solution (1.3 mL, 11mmol), and p-tolualdehyde (1.6 mL, 10 mmol) were mixed and stirred at90° C. for 2 hours. After the reaction solution was cooled to roomtemperature, the yield of p-toluic acid by measurement of GLC was 42%.

Example 9

Nafion NR50 (500 mg), 30% aqueous hydrogen peroxide solution (1.3 mL, 11mmol), and p-anisaldehyde (1.2 mL, 10 mmol) were mixed and stirred at90° C. for 2 hours. After the reaction solution was cooled to roomtemperature, the yield of p-anisic acid by measurement of GLC was 4%.

Example 10

Nafion NR50 (500 mg), 30% aqueous hydrogen peroxide solution (1.3 mL, 11mmol), and 10-undecenaldehyde (2.1 mL, 10 mmol) were mixed and stirredat 90° C. for 2 hours. After the reaction solution was cooled to roomtemperature, the yield of 10-undecenoic acid by measurement of GLC was90%.

INDUSTRIAL APPLICABILITY

According to the production process of the present invention, usefulcarboxylic acids to be widely used as intermediate for various organiccompounds can be obtained under mild conditions and in high yields.Moreover, since the process of the present invention does not use anyorganic solvent, acid, and base, the reaction operations are simple andthe operation for solvent removal after the completion of the reactionis not required as well as the recovery and reuse of the catalyst arepossible, the influences and toxicity on the environment and a humanbody are very little, and the process also has an effect of reducing aburden on the environment, so that carboxylic acids can be obtainedsafely, simply, and efficiently.

1. A process for producing carboxylic acid, which comprises reactingaldehyde-containing oily solution with an aqueous hydrogen peroxidesolution in the presence of a catalyst comprising a polymer compoundhaving a sulfonic acid group in a side chain thereof in a heterogeneoussolution system.
 2. The process for producing carboxylic acid accordingto claim 1, wherein the polymer compound is at least one polymerselected from a styrene polymer, a copolymer of styrene anddivinylbenzene, and a fluorocarbon polymer.
 3. The process for producingcarboxylic acid according to claim 1, wherein the aldehyde is a compoundrepresented by the following formula (1):RCHO  (1) wherein R represents a monovalent group selected fromhydrogen, an alkyl group, a cycloalkyl group, an aryl group, and anaralkyl group.